Commit 01b2a521 authored by Steven Rostedt (Google)'s avatar Steven Rostedt (Google)
Browse files

tracing: Add ioctl() to force ring buffer waiters to wake up 

If a process is waiting on the ring buffer for data, there currently isn't
a clean way to force it to wake up. Add an ioctl call that will force any
tasks that are waiting on the trace_pipe_raw file to wake up.

Link: https://lkml.kernel.org/r/20220929095029.117f913f@gandalf.local.home



Cc: stable@vger.kernel.org
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Fixes: e30f53aa ("tracing: Do not busy wait in buffer splice")
Signed-off-by: default avatarSteven Rostedt (Google) <rostedt@goodmis.org>
parent f3ddb74a

kernel/trace/trace.c

+22 −0
Original line number Diff line number Diff line
@@ -8349,12 +8349,34 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos, 
	return ret;

}



/* An ioctl call with cmd 0 to the ring buffer file will wake up all waiters */

static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned long arg)

{

	struct ftrace_buffer_info *info = file->private_data;

	struct trace_iterator *iter = &info->iter;



	if (cmd)

		return -ENOIOCTLCMD;



	mutex_lock(&trace_types_lock);



	iter->wait_index++;

	/* Make sure the waiters see the new wait_index */

	smp_wmb();



	ring_buffer_wake_waiters(iter->array_buffer->buffer, iter->cpu_file);



	mutex_unlock(&trace_types_lock);

	return 0;

}



static const struct file_operations tracing_buffers_fops = {

	.open		= tracing_buffers_open,

	.read		= tracing_buffers_read,

	.poll		= tracing_buffers_poll,

	.release	= tracing_buffers_release,

	.splice_read	= tracing_buffers_splice_read,

	.unlocked_ioctl = tracing_buffers_ioctl,

	.llseek		= no_llseek,

};